DESCRIPTION (Applicant's Description): Variation in the activity and/or abundance of transcription factors is generally acknowledged to be a regulatory nexus where signaling cascades converge and are transduced into specific cellular responses. Changes in transcription factor activities provide some of the clearest examples of our insights into the etiology of cancer and many other diseases. The studies outlined here focus on the activities of GATA-2 and GATA-3, two transcription factors we discovered a more than a decade ago, and through these studies we propose to determine how these vital transcriptional modulators exert their demonstrably profound regulatory effects during embryonic development. Through targeted mutagenesis in mice, five of the six vertebrate Gata factor genes have been shown to be required for embryonic survival. Since the Gata2 and Gata3 germ line mutations result in early to mid-embryonic lethality, it has previously been impossible to examine the functional role these proteins play in organs and tissues that are formed after the mutation-induced embryonic demise. In order to understand problems that might arise in late embryonic or adult cell lineages due to these mutations, we continue to develop strategies for gene rescue based on the generation of animals in which the mutant alleles are complemented by transgenic YACs or BACs encoding GATA-2 and GATA-3. In the first strategy, we propose to define the transcriptional regulatory elements that confer tissue-specific regulation to the GATA factor genes, and to then generate partially complementing alleles (by deletion of specific tissue regulatory domains from a fully complementing YAC) to allow the analysis of GATA factor function in specific cell lineages, while at the same time conserving all epistatic relationships or inductive effects from nearby tissues that express the same factor. These studies should shed important new insights into the question of functional redundancy between closely related regulatory proteins expressed in overlapping tissues and times during embryonic development, and how individual GATA proteins contribute to determination and differentiation in several cell lineages (in discrete subsets of CNS neurons, in hematopoietic cells and in the kidney).